[The frequency-contrast sensitivity of visual stimulus perception in patients with schizophrenia with the therapy of atypical and typical antipsychotic drugs].

We studied the effect of typical and atypical antipsychotics drag treatment on the perception of visual stimulus which activates preferentially different visual channels. We recorded contrast sensitivity in normal and schizophrenic patients. Elements presented with Gabor-like gratings with sinusoidal distribution of brightness, spatial frequency: 0.

[The efficiency of recognition of the size of segments of line by the observers with different parameters of the cognitive style].

We estimated efficiency of recognition of the size of segments of line by the persons with different parameters of cognitive style: the field dependence--field independence, the analytically--synthetically style, the flexible--rigid cognitive control. The size of segments of line was judged in task of the magnitude of the Ponzo illusion measurements. It was established, that the magnitude of the Ponzo illusion significantly less in subjects with the field independence cognitive style, than with field independence.

[The contrast sensitivity in schizophrenia with different durations disease].

We recorded contrast sensitivity in normal and schizophrenic patients. We presented Gabor gratings with sinusoidal distribution of brightness, with the spatial frequency: 0.4 cycles/degree, 3.

[Study of parvocellular and magnocellular visual channels in normal subjects and in patients with psychopathology].

We measured susceptibility to the Müller-Lyer illusion in schizophrenic patients and normal observers. The images of the Müller-Lyer figure were digitally filtered in a high-frequency and low-frequency band by wavelet filter. Patients with schizophrenia are more susceptible to Müller-Lyer illusion, than mentally healthy examinees.

[Features of perception of length of segments under conditions of ponzo and Müller-Lyer illusions in schizophrenia].

In order to better appreciate the neurophysiologic mechanisms of perception of length under conditions of geometrical visual illusions, we studied sensitivity of mentally healthy subjects and schizophrenic patients to Ponzo and Müller-Lyer illusion. Patients with schizophrenia estimated length of segments of Müller-Lyer figure less precisely. Accuracy of perception of length of segments in Ponzo figure was ambiguously connected with the duration of the disease.

[Electrophysiological and psychophysical studies of the effect of duration of presenting textures on the recognition threshold].

We studied the dependence of correct response number, response time, and the main characteristics of visual evoked potentials on the time of the stimuli presenting. The coincidence of the recognition temporal thresholds and occurrence of differences in the visual EPs suggests that the temporal characteristics of these processes differ in different subjects. Two groups of observers were distinguished with different temporal characteristics of perception and the EP development.

[Incomplete 2-D images perception at viewpoint variation of 3-D objects].

Thresholds of recognition of 3-D objects when viewed as incomplete 2-D images were measured in psychophysical experiments varying perspective of 3-D objects during subject's learning and testing. The new method of measurement of recognition thresholds of the 2-D incomplete images of 3-D objects in Gollin-test has been created. The visual system appears to be capable of extrapolating results that were obtained at the first presentation of object, at one viewing angle to other, subsequent viewing angles.

[Investigation of the perception of incomplete contour figures of the various size].

The purpose of the current research was to estimate the range of angular sizes of incomplete images across which the perception of the given images does not depend on scale. We have measured thresholds of recognition of the identities of objects across a wide range of angular sizes from 0.19 to 50 degrees of visual angle.

[Analysis of fragmented images perception: local features and global description].

Analysis of experimental investigations of the perception of incomplete images is presented. It illustrates two different approaches to work of the brain mechanisms involved: one approach is based on the perception of whole images and another on local informative features. These approaches describe two different mechanisms, which are possibly used by brain systems for incomplete image recognition.

[Human magno- and parvo-systems and selective disruptions in their function].

In psychophysical and electrophysiological investigations, we tested the hypothesis that in patients with multiple sclerosis at its early stage either phasic cells of the magnocellular pathway or tonic cells of the parvocellular pathway are disturbed. Healthy humans and patients with early stage of diseases have a contrast spatial-frequency sensitivity measure. The decrease in sensitivity at low, medium and high spatial frequency indicates changes in parvo- and magno-system activity.

[Localization of human brain areas activated for chaotic and ordered pattern perception].

The aim of our work was to localize cortical areas involved in the processing of incomplete figures using functional MRI (fMRI) for 8 healthy volunteers (18-30 year old) with the did of anatomical and fMRI fast imaging technique: echo planar imaging (EPI), whole brain scan (36 slices) matrix 64 x 64, 3.7 second. We used 1.

[Electrophysiological investigation of the texture discrimination mechanisms].

In electrophysiological and psychophysical experiments, we investigated mechanisms of the visual system underlying local and global texture processing. Textures included rectangular matrixes composed of Gabor patches (sine wave grating windowed by a Gaussian envelope). Orientation of each grating varied from 0 to 165 degrees with the step of 15 degrees.

[Visual mechanisms of recognition of vanishing figures].

The acuity test Landolt C's with a complex contour imitating various kinds of high-pass spatial frequency filtering generated as a printed visual acuity charts with a grey background were studied with regard to recognition thresholds. Comparisons were made for recognition thresholds with different complex contours. When the vanishing optotypes are out of focus, their image on the retina fades rapidly into the grey background, rendering them invisible rather than merely blurred as in the standard chart.

[Objective measurements of visual acuity by visual evoked potentials].

Electrophysiological measurements of the threshold spatial frequency were conducted in 26 healthy subjects by using visual evoked potentials with the purpose of objective determination of the visual acuity. For that we proposed a universal method of the visual stimulation and EEG processing (using ICA decomposition in particular) to minimize errors arising on account of individual differences in the visual system functioning. As a result, a correlation of 0.

[Signal/noise ratio at the visual recognition threshold of incomplete figures].

We measured recognition thresholds of incomplete figure perception (the Gollin test). This test we regarded as a visual masking problem. Digital image processing permits us to measure the spatial properties and spatial frequency spectrum of the absent part of the image as the mask.

[Visual potentials in humans with multiple sclerosis evoked by checkboard pattern of different contrast with additional noise].

A hypothesis is advanced of an effect of internal noise upon signal conduction along visual nerve in an early stage of multiple sclerosis. Visual evoked potentials in response to chess patterns against a homogeneous background and against a noise background were studied in healthy subjects and in patients with multiple sclerosis. Contrast between internal noise in the patients was found to be twice as great as in healthy subjects.

[Efficiency of a visual system under conditions of uncertainty of the appearance of a moving object].

The effect of uncertainty of a moving object appearance in the noise field upon the coefficient efficiency, we studied. At short durations of presentation (40-80 msec) and high level of external noise, this effect was maximal: magnified 100 times. The efficiency coefficient dependence on the duration of a moving object presentation was shown to be characterized by two maximums.

[Optical-geometrical parameters and perception threshold of the fragmented contour figures].

The thresholds of recognition of line drawings of common objects were measured using the Gollin-test procedure, in which separate random line fragments are displayed cumulatively up to the point of recognition. It was shown that the mean percentage of contour displayed at threshold recognition for different images was always about 12.5%, despite inter-subject variability between 5% and 25%.

[Principle of least action, physiology of vision, and conditioned reflexes theory].

The variation principles such as principle of least action by Maupertuis (1740) and Fermat principle (1660) are fundamental for physics. They permit to establish a property by which the actual state is differing from all possible states of the system. The variation approach permits to establish equation of motion and equilibrium of a material system on the basis of one common rule which reduces to the search of the function extremes, describes this property of the system.

[The resolution and discrimination of images in the visual system].

We analysed the conformity of optic and retinal cones anatomy factors by the two-point test. Obtained by F. Campbell and R.

[Visual evoked potentials in response to dichoptic presentation of sinusoidal grating and noise background].

Dichoptic stimulation was used in comparison of visual evoked potentials (VEPs) with those obtained with monocular stimulation (recordings made from the occipital area). 16 subjects viewed sinusoidal gratings with the right eye while a visual noise was added via a mirror for the left eye. In presence of the noise, amplitude of the early VEP components' N1, P1b, and the late component P2 decreased, P1a is not changed in presence of the noise, and the late negative wave N2 increased for all spatial frequencies.